Merge xfs branch 'iomap-4.19-merge' into linux-gfs2/for-next.  This
brings in readpage and direct I/O support for inline data.

The IOMAP_F_BUFFER_HEAD flag introduced in commit "iomap: add initial
support for writes without buffer heads" needs to be set for gfs2 as
well, so do that in the merge.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>